1. Field of the Invention
The present invention relates to a passive optical network, and more particularly to a passive optical network including a light source which can generate wavelength-seeded optical signals.
2. Description of the Related Art
Passive optical networks, generally, include a central office for providing a communication service, a plurality of optical network units for receiving the communication service, and at least one remote node for relaying the communication service between the central office and the optical network units. The central office and the remote node(s) are typically linked to each other through an optical fiber, and the remote node and each of the optical network units are linked to each other through a distinct optical fiber, thereby forming a double-star structure.
The conventional passive optical network typically employs a wavelength-division-multiplexing (WDM) optical communication scheme. According to the WDM passive optical network, mutually different wavelengths of light are allocated to the optical network units and data are transmitted/received by using optical signals onto which the data are loaded. Such a wavelength-division-multiplexing scheme has advantages in that it is easy to maintain security and to expand existing communication lines to include additional optical units.
The conventional passive optical network typically includes a downstream light source for generating a downstream optical signal provided from the central office to each of the optical network units, and upstream light sources for generating upstream optical signals transmitted from each of the optical network units to the central office.
The downstream and upstream light sources each include a reflective semiconductor optical amplifier and a Fabry-Perot laser capable of generating wavelength-seeded light, which have a direct modulation function.
However, the light source, typically using a wavelength-injection scheme, has a problem in that the central wavelength of a downstream or upstream optical signal moves toward a longer wavelength side due to its non-linearity characteristic of semiconductor optical amplifier and positive chirp occurring during direct modulation. The positive chirp illustrates a phenomenon in which the wavelength of an optical signal generated from a light source moves toward a longer wavelength side. Such movement in the central frequency or wavelength operates to deteriorate the performance of the whole network.